C#

using System.Runtime.InteropServices;

[DllImport("shell32.dll", CharSet = CharSet.Auto)]
static extern bool ShellExecuteEx(ref SHELLEXECUTEINFO lpExecInfo);

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
public struct SHELLEXECUTEINFO
{
    public int cbSize;
    public uint fMask;
    public IntPtr hwnd;
    [MarshalAs(UnmanagedType.LPTStr)]
    public string lpVerb;
    [MarshalAs(UnmanagedType.LPTStr)]
    public string lpFile;
    [MarshalAs(UnmanagedType.LPTStr)]
    public string lpParameters;
    [MarshalAs(UnmanagedType.LPTStr)]
    public string lpDirectory;
    public int nShow;
    public IntPtr hInstApp;
    public IntPtr lpIDList;
    [MarshalAs(UnmanagedType.LPTStr)]
    public string lpClass;
    public IntPtr hkeyClass;
    public uint dwHotKey;
    public IntPtr hIcon;
    public IntPtr hProcess;
}

private const int SW_SHOW = 5;
private const uint SEE_MASK_INVOKEIDLIST = 12;
public bool ShowFilePropertiesDialog(string fileName)
{
    SHELLEXECUTEINFO info = new SHELLEXECUTEINFO();
    info.cbSize = System.Runtime.InteropServices.Marshal.SizeOf(info);
    info.lpFile = fileName;
    info.lpVerb = "properties";
    info.fMask = SEE_MASK_INVOKEIDLIST;
    info.nShow = SW_SHOW;
    return ShellExecuteEx(ref info);
}

ShowFilePropertiesDialog(@"C:\hello.txt");

anurag3487 wrote:

The conversion into months in negative scenario is what I am not getting.

PIEBALDconsult wrote:

you must take the varying lengths of months and Leap Days and into account.